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Re: [Amps] Henry 3kA Choke input Pwr Supply Overvoltage Query

To: <Amps@contesting.com>, <w2cqm@juno.com>
Subject: Re: [Amps] Henry 3kA Choke input Pwr Supply Overvoltage Query
From: "Jim Tonne" <tonne@comcast.net>
Date: Fri, 18 Nov 2005 09:25:55 -0500
List-post: <mailto:amps@contesting.com>
Would place money the filter choke has shorted turns.
This happened to me with a broadcast transmitter years
ago.
- Jim Wb6BLD

----- Original Message ----- 
From: <w2cqm@juno.com>
To: <Amps@contesting.com>
Sent: Friday, November 18, 2005 9:21 AM
Subject: [Amps] Henry 3kA Choke input Pwr Supply Overvoltage Query


> Since I'm relatively unfamiliar with the characteristics of a vintage 
> Henry 3KA choke input power supply, perhaps someone would comment on a
> question that has arisen regarding what appears to be  too high an output
> plate  voltage. The Henry is equipped with a 10Hy fixed choke tuned with
> a .1mFd @ 7500VDC capacitor. The diode configuration is full wave bridge
> with the choke wired in series and situated before the filter capacitor;
> for a typical choke input circuit. All components are OEM Henry.  A Plate
> transformer output is 3300VAC with a nominal  input rating of 230VAC.
> There's a 4  terminal manual step start power up switch (position 1-off),
>  voltage fed through resistance wire in position 2 for the soft start, 
> a  CW tap (position 3 which shorts out the resistance), and a  third SSB
> tap, position 4.  In the no load  CW position, DC voltage is over 4KV and
> in the SSB (higher tap) position the plate voltage is close to 5KV. 
> Henry only provides a  full scale plate meter calibrated for 4KV so the
> dial deflection obviously   is off scale. These high voltage values are
> verified independently  with a calibrated  Triplett  meter. In addition,
> they appear to be significantly  higher than  the levels suggested in the
> operator's manual.  Tested the choke for resistance (about 56 ohms) and
> the tuning capacitor is not shorted. My primary voltage is somewhat
> higher (248VAC) so that may account for some of the overvoltage. However,
> to my mind, the resulting operating voltage is at least 800-900VDC too
> high and of course is causing some concern. I've verified that the wiring
> is correct and I'm asking for any comments that may explain the higher
> levels of plate voltage. Any comments would be appreciated. Ron W2CQM/3
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